Wiring EMI filter in laser

Lasers
1

I bought an EMI filter for the monocle and I’m wondering about the best way to wire it.

My default assumption is to wire it as close as possible to the LPS to clean up power for everything else in the machine. Is there any reason that’s a bad choice?

2

If you’re expecting noise on the AC line and that’s what your looking to protect from then I would put it on the AC input/plug connector. That won’t help anything else if the LPS is throwing noise around but if you power other PSUs from the same AC line it should help unless the LPS is emitting back on the AC line.

3

I thought that the LPS emitting on the AC line was the main point of adding an EMI filter, and that I wanted it between the LPS and the LV (24V) PS? My input power is pretty clean, I think. I suppose it might be less clean if I’m running other shop tools, but if I’m running the laser I definitely should not be using the lathe at the same time. :relaxed:

4

That makes sense to me since your LV PS is what powers your control system(s). I didn’t know if you had known noise on your AC powerline to the machine itself. If it’s a smallish module then I would probably mount it internally on a wall near the LV PS. Having it visible inside like that you’ll also be reminded of the filtering if you start having to chase down goblins trying to make your day difficult.

5

All my electronics are in the back.

The HV side is on the right, with the LPS being mounted directly below the anode. The LV side is on the left, underneath the cathode. I was planning to mount the EMI right next to the LPS on the HV side so that the HV supply wires aren’t an antenna. But this is outside my area of expertise.

6

Not sure what problem you are trying to solve?

Here is my experience with line filters & K40 noise:

  1. Most line filters are used to keep mains noise out of the machine vs noise isolation inside the machine.
  2. These filters are for conducted noise not radiated. I have seen mains noise from shop machines penetrate a K40 and cause controller problems. I suspect this was exacerbated by poor internal grounding and the lack of an input filter on the mains.
  3. I have never found the LPS to inject noise through its AC line to the LVPS mains.
  4. Most LPS noise comes from radiated noise from arcs and corona. Nothing can filter it, you have to stop the arc.
  5. Most if not all K40 noise problems I have worked on are the result of poor grounding design + arcs and corona.

If you are concerned about the LPS AC side injecting into the LPS AC side then use 2x filters. One one is the input of each. I would wait until you have a problem before using this method.

That said, I would put one mains filter on the input and then pay attention to the grounding design.

7

The only problem I have now is that I have been working intermittently on this for a couple years and I still haven’t fired the laser.

I had read somewhere (it was long ago) that these filters were recommended, and my memory for why was incomplete and imperfect.

I’m glad I asked. Thank you!

8

I know the feeling. I have a 2023 resolution to clear out all my part-done projects. Wow, there are a lot! My problem is I like to solve problems and when I prove it’s solved I lose interest and the final thing sits in a project box.

3 Likes